(1) Field of the Invention
This invention relates to a covulcanizable rubber composition comprising (1) a partially hydrogenated unsaturated nitrile-conjugated diene copolymer, (2) an ethylene-propylene copolymer and (3) at least one material selected from the group consisting of an ethylene-vinyl acetate copolymer, an acrylic rubber and a halogenated butyl rubber. It further relates to rubber articles made by shaping and vulcanizing the rubber composition.
(2) Description of the Related Art
A partially hydrogenated unsaturated nitrile-conjugated diene copolymer (hereinafter abbreviated to "HNBR") is well known as a rubber having good heat-aging resistance, oil resistance and rancid gasoline resistane. To utilize these good characteristics and impart other characteristics to this rubber, proposals have heretofore been made wherein the copolymer is blended with other rubbers. Among the rubber blends, a blend thereof with an ethylene-propylene copolymer (hereinafter abbreviated to "EPM") is well known as a rubber composition having good heat-aging resistance, oil resistance and weather resistance (Japanese Unexamined Patent Publication No. 58-40332, 61-40342, 61-283639 and 62-190241). However, the partially hydrogenated unsaturated nitrile-conjugated diene copolymer rubber and EPM have greatly different solubility parameters and hence, when mixed together, it is almost impossible that they form a uniformly dispersed mixture. Further, these copolymer rubbers exhibit different rates of vulcanization, and therefore, properties of a vulcanized rubber from the composition of these copolymer rubbers are restricted. Especially, the constant-elongation fatigue properties are poor.